The present invention relates to an industrial vehicle having a hydraulically-operated braking device and a hydraulically-operated loading device.
Japanese Patent Application Publication No. 2002-114499 discloses a forklift truck as an industrial vehicle having a hydraulically-operated device. In the forklift truck according to the above Publication, hydraulic pressure is accumulated in an accumulator and such pressure is released to operate the hydraulic device. The hydraulic mechanism of the forklift truck includes an open center control valve that provides fluid communication between an hydraulic pump and an oil tank when there is no instruction for operating loading device of the forklift truck. The provision of such an open center control valve allows hydraulic pressure to be accumulated in the accumulator by driving the hydraulic pump in the absence of instruction for operating the loading device.
In recent years, in order to reduce the difference in load handling speed between working with no load and working with maximum load, it has been contemplated to use a hydraulic mechanisms having a closed center control valve which blocks the fluid communication between the hydraulic pump and the loading device in the absence of instruction for operating the loading device. The hydraulic mechanism having the closed center control valve also has a pressure compensating valve. The pressure compensating valve compensates for the operating pressure for hydraulic cylinder for operating the loading device and also releases the pressure in the oil tank when the pressure of a circuit exceeds the relief pressure. In the hydraulic mechanism having the closed center control valve, driving the hydraulic pump in the absence of an instruction for operating the loading device does not cause the accumulator to operate for accumulation because the pressure in the circuit is released in the tank through the pressure compensating valve. Therefore, in using a hydraulic mechanism having a closed center control valve, the configuration in which pressure is accumulated in the accumulator needs to be reconsidered.
The present invention which has been made in light of the problems described above is directed to providing an industrial vehicle in which accumulated pressure in an accumulator is maintained properly.